Detecting Planets via Gravitational Microlensing -- Toward a Census of Exoplanets Subo Dong Institute for Advanced Study Collaborators: Andy Gould (Ohio State) [MicroFUN], Andrzej Udalski (Warsaw) [OGLE], J.P. Beaulieu (IAP) [PLANET], Ian Bond (Massey) [MOA], Keith Horne (St. Andrews) [RoboNet]
Stamp collecting microlensing planets Beaulieu et al 2006 Preliminary (C. Han) Gould & Loeb (1992) Planetary Caustics: Short blip anywhere on the light curve ~5.5 M Earth A peak ~ 3 Bond et al 2004 ~14 M Earth A peak ~ 8 Gaudi et al 2008 Mao & Paczynski (1991) Resonant Caustics: Planet very close to Einstein Radius, Long time-scale perturbation, complicated deviations ~830 M Earth A peak ~ 8 ~86 M Earth A peak ~ 290 Udalski et al 2005; Dong et al 2009 Gould et al 2006 Griest & Safizadeh (1998) Central Caustics: Perturbations close to the peak of High-Magnification Events ~1200 M A peak ~ 40 ~13 M Earth A peak ~ 800
Planetary Microlensing Mao & Paczynski (1991) Gould & Loeb (1992) -- Most sensitive to planets within from ~0.6 to ~1.6 r E (Einstein Radius: r E = θ E D L ~ 3 AU) > Solar System Analogs! Short timescale: t planet /t E ~ M planet /M star q d q Survey (OGLE, MOA): Finding microlensing events + Follow-up (MicroFUN, PLANET, RoboNET): Intensive 24hr Monitoring of a Selective Number of Events Credit: B. S. Gaudi
A Classic Gould & Loeb event First Gould & Loeb type planet: q ~ 8 x 10-5 d ~ 1.6 A cool Neptune: ~5.5 M Earth, 2.6 AU, T~50K! OGLE-2005-BLG-390 (Beaulieu et al. 2006, Nature, 439, 437)
Gould & Loeb Event -- Minor Image Credit: B. S. Gaudi
MOA-2009-BLG-266 The latest planet found by MOA + MicroFUN/PLANET q = 5 x 10-5 d = 0.9 M p ~ 14 M Earth Credit: C. Han
Extrasolar Jupiter vs. Neptune Gaudi et al. (2002) NO planets from 43 events well observed by PLANET collaboration (1995-2000) : < ~30% Jupiter around M dwarfs (at 95% conf) First Gould & Loeb type planet: A cool super Earth: ~5.5 M Earth, 2.6 AU, T~50K! OGLE-2005-BLG-390 (Beaulieu et al. 2006) Small Number statistics, but implies: Cold Neptunes Are Common! ~40% (16% - 69% at 90% conf) (Gould et al. 2006)
Why Microlensing? Planets down to Earth mass at a few AU (close to and beyond the snow line) Host stars from M to G dwarfs + white dwarfs, brown dwarfs at ~1 8 kpc (even potentially in M31) Free floating planets (Juric & Tremaine 2008) Janczak, Fukui, Dong et al., 2009, ApJ, Submitted, arxiv:0908.0529
Credit: B. S. Gaudi
Planetary Caustics Credit: C. Han
Resonant Caustics
Central Caustics and High-magnification Events High Magnification Event [A > ~50] (Central Caustic Perturbation) Griest & Safizadeh (1998) Great sensitivity to planets at all angles over the peak (Detection & Exclusion); multi-planet (Gaudi, et al, 1998, ApJL, 502, L33) Relatively easy to monitor as the peak can be alerted in advance
Planetary Detection Efficiency of Extremely High-magnification Event OGLE-2004-BLG-343 Dong et al, 2006, ApJ, 642, 842 -- Comments by Virginia Trimble et al, Astrophysics in 2006: But we begin with honest appreciation of honest authors (ApJ 642, 842) who explain that due to human error, intensive monitoring did not begin until 43 minutes after peak magnification A max ~ 3000, no planet signatures What planets could have been detected?
Physical Detection Efficiency
Lesson Learned! Unit: 3.2AU A max ~ 1600 Yee, Udalski, Sumi, Dong et al, 2009, ApJ, 703, 2082
The most massive M-dwarf planet? Lens + Source Microlens Parallax + HST photometry & astrometry M = 0.46 ± 0.04 M D lens = 3.2 ± 0.4 kpc M p = 3.8 ± 0.4 M J at 3.6 ± 0.2 AU Discovery: Udalski, A. et al. 2005, ApJL, 628, 109 Characterization: Dong, S. et al. 2009, ApJ, 695, 970
The first Jupiter/Saturn Analog: OGLE- 2006-BLG-109 A scaled version of our Solar System b: ~0.71 Jupiter Mass at ~2.3 AU c: ~0.27 Jupiter Mass at ~4.6 AU M * ~ 0.5 M Gaudi et al, 2008, Science, 319, 927
OGLE-2006-BLG-109Lb
Planet Found in Severe Finite-source effects: MOA-2007-BLG-400 Dong, S., et al., 2009, ApJ, 698, 1826
MOA-2007-BLG-400 Dong, S., et al., 2009, ApJ, 698, 1826
MOA-2007-BLG-400 A buried planet mass ratio: q=0.0026 +/ -0.0004 Dong, S., et al., 2009, ApJ, 698, 1826
MOA-2008-BLG-310Lb, a Bulge planet candidate Janczak, Fukui, Dong et al., 2009, ApJ, Submitted, arxiv:0908.0529 E M lens rel 0.16 0.01mas D lens 6.0kpc (If M lens > 80 M J ) VLT NACO -> M ~ 0.67 ± 0.14 M 74 M earth at 1.25 AU
Challenges in Modeling High-mag Events Sometimes little intuition in initial guesses Is the model unique? Systematically Search the Complex Parameter Space But: computationally very expensive (finite-source)
An Efficient and Robust Algorithm Dong, S., et al., 2006, ApJ, 642, 842 (Appendix A) Dong, S. et al., 2009, ApJ, 698, 1826 (Hexagon-cell Magnification) Map-Making (workhorse): Loop-Linking (backup)combin es contour integration and ray-shooting shoot rays from a narrow annulus on the image plane - reduce the overhead by orders of magnitude on the source plane, a combination of pixels and rays, with enhanced speed while preserving accuracy
Next-gen Survey in ~5 years A global ~2m wide-field telescope network A few thousands events per year with 10-20 min cadence, no human interference (solid statistics) ~40 η Earth and 1-2 order of magnitude more Neptunes and Jupiters in 5-yr survey plus free floating planets Many more high-mag events (information rich: multi-planet system, high-order effects like orbital motion etc.)
Thank you!